The studies proposed in this application are designed to explore the mechanisms by which environmental variables modulate reproductive function in mammals. Specifically, the immediate goals of the proposed work are to explore the effects of reduced caloric intake. Experimental models will include prepubertal and adult female and pubertal male rats. Experiments are designed to test the hypothesis that reduced caloric intake may produce endocrine defects at multiple points in the hypothalamic-pituitary- gonadal axis. Within the framework of this hypothesis we will examine the nature of the altered feedback of gonadal steroids on gonadotropin secretion in the underfed organism and the abnormal pituitary response to gonadotropin releasing hormone (GnRH). The following studies are proposed. First, the pattern of gonadotropin secretion will be compared between food restricted (R) and control (C) animals with respect to pulse height and frequency. Secondly, we will examine the time-related changes in these patterns following manipulation of circulating gonadal steroid hormone levels by castration and steroid hormone replacement. Thirdly, a study will be conducted to examine the nuclear estrogen receptor activities of the hypothalamus and pituitary glands of R and C prepubertal and adult female rats. Transformation (translocation) and replenishment times will also be examined. Fourthly, a study will be conducted to examine in detail the response of pituitaries from R and C rats to gonadotropin-releasing hormone (GnRH) both in vivo and in vitro. This study will also examine the effects of altered gonadal steroid hormone levels on the GnRH induced gonadotropin secretion and the ratios of luteinizing hormone (LH) to free LH alpha subunit released in R and C rats following GnRH stimulation. The main thrust of these studies is to examine in animal models the effects of nutritional deficiencies and provide answers to the reproductive and sexual disturbances observed in such health-related problems as anorexia nervosa.